Wandering Temp gauge

[krisnowicki]

I have a cruiser with an alpha one drive and 86 260 mercruiser engine. I have a temp guage that goes from 200 to 120 over and over. I put my hand on the risers and they are never hotter than I can bare to touch. How can I test the guage or sender? It would think it has to be one of them. It will rise to 200 sit there for 1 mins then drop to 130 in 1 or 2 secs ... over and over. I changed the thermostat to no avail

 

[o/b tech]

Re: Wandering Temp gauge

Check for a loose connection at the back of the gauge or sender. Hope the info helps.

 

[Bondo]

Re: Wandering Temp gauge

Ayuh,... I'd change the T-Stat,... An 80? swing is Extreme,+ outa line with what's expected...

 

[mciaio]

Re: Wandering Temp gauge

That is a typical symptom of a slow acting thermostat, but you changed it. I would check engine grounds, make sure they are clean and tight. Any other gauges fluctuating? It could be in the electrical system.

Do you have access to a infrared temp. gun? I would "shoot" the thermostat housing on the engine to see if the temp. gun agrees with your gauge. I'm thinking it may be a restriction of some type in the water circulatory system. Maybe a bad circ pump?

 

[krisnowicki]

Re: Wandering Temp gauge

The impeller and themorstat are new. I will check flow tommorrow, I dont understand how it would swing 80 degress in like 2 secs...

 

[mciaio]

Re: Wandering Temp gauge

Keep in mind there are two water pumps on that unit. The raw water pump in the drive and the circ pump on the front of the engine.

Agreed... if the water level is going up and down inside the block, that might account for your change.

 

[Fun Times]

Re: Wandering Temp gauge

The impeller and themorstat are new. I will check flow tommorrow, I dont understand how it would swing 80 degress in like 2 secs...

When you installed the gasket between the thermostat housing and the intake manifold did you use any kind of gasket sealant on it, Or did you put it on dry???

 

[JustJason]

Re: Wandering Temp gauge

I dont understand how it would swing 80 degress in like 2 secs...

Engine temp doesn't swing that fast. Check all the electrical. I would suspect the sender is good, but it may have a poor connection. Or poor power/ground/signal wire connections at the gauge, or a bad gauge itself.

 

[krisnowicki]

Re: Wandering Temp gauge

the gauges are old and the problem looks electrical. I can put my hand on the engine and sender at all times. I am guessing the guage I am going to swap it with one i have in my garage and give it a go first.

I replaced everything with new gaskets on the therm housing. I put veeything on dry.

 

[JustJason]

Re: Wandering Temp gauge

Easy test,

Put your multimeter on ohms. Ground 1 end the same place the gauge gets its ground, and put your positive on the sender wire that goes into the gauge. Now you will be seeing the same resistance that the gauge sees. I don't know what the value is supposed to be without digging it up, but either way, If your resistance stays somewhat constant but the needle on the gauge is flipping out, you can go ahead and replace the gauge at this point. If the resistence is all over the place, then start with the wiring and work your way backwards.

 

[Silvertip]

Re: Wandering Temp gauge

It can swing 80 degrees because dumping water that is 130 degrees colder than the water in the block has a "chilling effect". Assuming the raw water is 70 degrees and the block temp is 200 -- that leaves a 130 degree differential. That will cool things down in a hurry. Just because you changed the stat does not mean you changed it properly or with a good one or that there is not another issue.